Environmental filtering drives community specific leaf area in Spanish forests and predicts relevant changes under future climatic conditions

How functional traits at community level relate with environmental conditions is of great relevance to assess potential effects of climate change on ecosystem functioning. Species' specific leaf area (SLA) is well recognised to be closely correlated with species drought resistance and with other forest functions such as productivity. Here, we used tree species abundance data from 44 501 forest plots from the Third Spanish National Forest Inventory and species SLA values from literature to assess how community weighted mean SLA (CWM) and SLA diversity within communities (FDis) of Spanish forests correlate with aridity. Later, using 19 climate change projections and following an approach that limits the values of CWM along an aridity gradient, we assessed the potential climatic effects on CWM for 2050 under the representative concentration pathways (RCP) 4.5 and 8.5. Results showed that CWM and FDis decreased significantly with aridity (deviance explained was 22 and 9%, respectively) suggesting an effect of climatic filtering at community level constraining the diversity of co-occurring strategies at harsher conditions. Up to 25% of plots were predicted to suffer changes in CWM with these impacts being more common and of a greater magnitude in communities characterised by a high CWM and located at humid and mid-altitude zones. Instead, communities already striving in arid areas appeared to be more resilient. The study proves useful for orienting forest management practices in current permanent forest stands based on trait ecology (e.g. promoting communities species composition with specific trait values), to increase their mitigation potential and adaptive capacity to current and future changing climate conditions.